1. Field of the Invention
The present invention relates to a powder material, an electrode structure, production processes thereof, and a secondary lithium battery, and more particularly to a secondary lithium battery which has an electrode structure comprised of a specific powder material and is high in capacity, and charging and discharging efficiency, and production processes of such powder material and electrode structure.
2. Related Background Art
It has recently been predicted that since the amount of carbon dioxide (CO2) gas contained in the air is increasing, the warming of the earth occurs due to a green house effect. For this reason, a new construction of a thermal power plant, from which CO2 gas is exhausted in plenty, has come to be difficult. Accordingly, there has been proposed, as an effective use of electric power generated by a generator in a thermal power plant or the like, the so-called load leveling in which night electric power is stored in a secondary battery installed in a general home, and this electric power is used in the daytime that power consumption increases, to level the load. It is also expected to develop a secondary battery having a high energy density as a secondary battery essential to electric cars having a feature that no air pollutant is exhausted. Further, it is of urgent necessity to develop a miniature, light-weight and high-performance secondary battery for a power source of portable equipment such as book type personal computers, word processors, video cameras and portable telephones.
Since an example where a lithium-graphite intercalation compound is applied to a negative electrode for a secondary battery was reported as such a miniature, light-weight and high-performance secondary battery in JOURNAL OF THE ELECTROCHEMICAL SOCIETY, 117, 222 (1970), the development of, for example, a rocking chair type secondary battery, or the so-called “lithium ion battery”, in which carbon (also including graphite) is used as an active material for negative electrode and an intercalation compound, in which a lithium ion has been introduced, as an active material for positive electrode, and lithium is intercalated between layers of carbon by a charge reaction to store it, has proceeded, and such a battery is in practical use. In the lithium ion battery, carbon of a host material between the layers of which lithium is intercalated as a guest material is used in a negative electrode, whereby dendrite growth of lithium upon charging is controlled to achieve a long life in a charging and discharging cycle.
In the lithium ion battery in which carbon is used as an active material for negative electrode, however, the cycle life is long, but its energy density does not reach that of a lithium battery in which metallic lithium itself is used as a negative active material.
Accordingly, carbon materials of still higher capacity to be used in a negative electrode of a lithium ion battery are extensively researched and developed. In order to realize a secondary battery having a higher energy density, it is essential to develop not only a material for a negative electrode, but also a material for a positive electrode having a higher capacity. Under the circumstances, lithium-transition metal oxide in which a lithium ion has been intercalated into an intercalation compound is mainly used as an active material for positive electrode. However, a discharge capacity of 40 to 60% of the theoretical capacity is only achieved. Therefore, there is also a strong demand for development of a positive electrode having a cycle life of practical levels and a higher capacity in secondary lithium batteries including “lithium ion battery” utilizing a lithium ion as a guest for charging and discharging.